World's worst internet virus

The world's worst computer virus is causing chaos for millions of people around the globe.

Dubbed Sobig-F, it is spread by email. It is believed that one in 17 of all electronic messages is now infected.

AOL claims to have stopped almost 12 million copies of the virus, which hijacks users' email address books and sends itself to every address it finds.

Experts believe the entire internet is slowly coming to a halt because of the vast numbers of emails it is creating.

They also warn that even more destructive viruses may be on the way.

Graham Cluley of anti-virus firm Sophos said: "This will almost certainly become the worst virus of all time, as people are suffering even if they don't have it. It's effectively slowly killing the internet by creating vast numbers of emails that clog everything up.

"We have had reports of home users finding several thousand copies of the virus in their inbox, while corporate systems are dealing with millions of copies of it. The incredible thing is that it's only been around for two days, we have never seen anything spread like this."

Sobig-F is believed to have originated from America and has already spread to 148 countries. Once on a machine, it attempts to give hackers access to your computer by downloading a small piece of software from its creator.

"It's basically turning your machine into a zombie that can be hijacked," said Mr Cluley. "We believe the people behind this could be trying to send as many junk emails as possible, and are turning every computer they come across into a junk email production centre."

Experts have already warned that Sobig-F may be only the beginning of a new assault on the world's computer systems by hackers. Several new versions of the virus, which has already been tweaked six times, are believed to be under development.

Mark Sunner is from Virus monitoring company MessageLabs. He said: "The Sobig virus writer's use of an in-built expiry date
indicates that he is committed to inventing new and improved versions. Each variant released so far has got worse, so we definitely expect more."

Computer users are being advised to ensure their antivirus software is up to date, which should protect them, and to remove the virus if their computer is already infected.

Users are being warned to be wary of messages bearing subject lines such as "Re: details", "Re: Thank You" or "Re: That movie". Computers reacting slowly are also a key sign that they may have the infection.

A second virus, the "white hat", yesterday brought Air Canada's booking and check-in operation to a standstill.

Many users are still recovering from the MSblaster worm, which last week took over almost 200,000 computers around the world. Experts have also advised people never to run programs sent to them via email, as they could potentially contain the virus.

It has been claimed that current internet security systems, which monitor all traffic going in and out of a corporate network are often adding to the problem. "People need to check their security settings, and stopping this virus spreading could be as simple as stopping program files coming into your company network via email," said Mr Cluley.

However, experts also tried to find a positive side to the crisis: "If anything good comes out of this, it might be that people will finally take internet security a bit more seriously, and know to never run software they receive via email," Mr Cluley added.